The State Route 520 Floating Bridge in Seattle, Washington


  • Cheryl L White Memorial University of Newfoundland


(ENGI 8751) (Case Study) (Civil) (Floating Bridge) (SR 520) (Concrete Pontoons) (Seattle, Washington) (Evergreen Point Bridge)


The four longest floating bridges in the world are located in Seattle, Washington on the North West Coast of the United States of America. At 2.3 km long and 35 m wide, the Evergreen Point Floating Bridge, also known as the State Route (SR) 520 Bridge, is the longest floating bridge in the world. Home to around 3.5 million people, the metropolitan area of Seattle is divided by Lake Washington and the SR 520 transports 115,000 vehicles across Lake Washington on a daily basis. At depths reaching 61 m [1] a suspension bridge would require a bridge tower of over 183 m; thus a floating bridge is necessary. Constructed in 1963, this bridge however is now approaching the end of its lifespan and will be replaced by an even longer and wider floating bridge by 2014. This paper will investigate why the bridge must be replaced, the past and current reasons for selecting a floating bridge to cross Lake Washington, what it takes to make a concrete bridge float, and how the new bridge will vary from the existing bridge.

Author Biography

Cheryl L White, Memorial University of Newfoundland

Civil Engineering Student


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Coastal and Ocean Engineering (ENGI.8751)